Mobile communication systems are becoming sophisticated and complicated from a 3.5-generation mobile communication system, which is widely used nowadays, that is, 3.5 G, to a 3.9-generation mobile communication system, that is, 3.9 G. Furthermore, it is expected that a fourth-generation mobile communication system, that is, 4 G service, will start. As mobile communication systems are becoming sophisticated and complicated in this way, a technique called a self organizing network (SON) has become a center of attention. The SON is a technique for automating and optimizing the installation, operation, and so on of mobile communication systems. In the future, a situation in which 3.5 G-, 3.9 G-, and 4 G-network systems are mixed will occur, as illustrated in FIG. 1. FIG. 1 is a diagram illustrating an example of the mobile communication system in which 3.5 G, 3.9 G, and 4 G are mixed. Actual examples include W-CDMA for 3.5 G, Long Term Evolution (LTE) for 3.9 G, and LTE-Advanced for 4 G.
Examples of the main functions of SON include self-configuration, self-optimization, and self-healing, as described below.
(1) Self-configuration function: the function of automatically, not manually, connecting to a network and setting adjacent cells, system parameters, and so on when a base station is to be deployed. This function may reduce man-hours and workload for the deployment.
(2) Self-optimization function: the function of automatically tuning a mobile communication system by adjusting a handover to an adjacent cell, adjusting the interference with an adjacent cell, and so on. This function is performed on the basis of measurement data collected at the nodes of the mobile communication system (that is, a base station, an exchange, a mobile station, and so on). Examples of the handover adjustment include adjustment of a threshold value for changes in wireless quality, which is used to determine whether to execute a handover. Examples of the interference adjustment include adjustment of transmission power in the individual cells and adjustment of transmission timing. This function may improve the communication quality of the mobile communication system.
(3) Self-healing function: the function of automatically detecting a problem in a mobile communication system and automatically specifying and analyzing the cause and restoring the system. This function may reduce man-hours and workload for maintaining the mobile communication system.
With a recent increase in mobile traffic and ecological awareness, effective use of wireless resources and reduction in the power consumption of the entire network by using the self-optimization function is becoming important.
For the effective use of the wireless resources, mobile stations are distributed to a plurality of cells in the relate art. This distributed processing is performed on the basis of the number of mobile stations under the control of a base station, throughput, and call connection load, measured by the base station. The distributed processing prevents decrease in throughput per mobile station due to concentration of the mobile stations to one cell. For example, there exists a method for moving, that is, handing over, a mobile station present in a macrocell to a microcell.
Examples of a method for achieving more effective use of the wireless resources are as follows: a first method is a method of control in consideration of not only the number of mobile stations, throughput, and call connection load but also the moving state or distribution of the mobile stations. In this method, a mobile station at rest is preferentially handed over to a microcell because a mobile station that is quickly moving at high speed goes out of a microcell. This allows the wireless resources to be stably utilized. A second method is a method of controlling not only handover but also the direction of radio waves transmitted from the base station and the transmission power in connection therewith. This method directs the radio waves to an area in which the density of mobile stations is high and increases the transmission power. This may increase the proportion of mobile stations having high wireless quality. Since a larger volume of data may be transmitted with the same wireless resources as the wireless quality increases, the use efficiency of the wireless resources may be enhanced.
Furthermore, the following control has conventionally been performed to reduce the power consumption of a network. Mobile stations are concentrated to a predetermined cell or sector. This concentration processing is performed based on the number of mobile stations under the control of a base station, throughput, and call connection load measured by the base station. This concentration processing may reduce electrical power for a base station corresponding to a cell in which the number of mobile stations has decreased as a result of movement of the mobile stations. For base stations having a separate processing unit for each sector, electrical power to be supplied to a processing unit corresponding to a sector in which the number of mobile stations is decreased may be reduced by concentrating mobile stations in a predetermined sector.
Related art is disclosed in Japanese Laid-open Patent Publication No. 2011-19039.